Coated articles demonstrating electromagnetic radiation transparency and method of mitigating contaminant build-up on a substrate

ABSTRACT

The present invention is directed to coated articles demonstrating a transmission of electromagnetic radiation having a frequency of 22 to 81 GHz in the range of 70% to 100%. The articles comprise substrates coated with curable film-forming compositions comprising a first film-forming polymer prepared from at least one hydrophobic monomer, a second film-forming polymer prepared from at least one hydrophobic monomer, and a curing agent. Upon application of the curable film-forming composition to the substrate to form a coating layer, the first film-forming polymer is distributed throughout the coating layer, and the concentration of the second film-forming polymer is greater at the surface of the coating layer than the concentration of the second film-forming polymer within the bulk of the coating layer. The present invention is also drawn to methods of mitigating contaminant build-up on a substrate using the curable film-forming compositions described above.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/038,505,filed Jul. 18, 2018, published as United States Patent ApplicationPublication Number 2020/0028528A1 and now allowed, which is incorporatedby reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to coated articles demonstratingtransparency to electromagnetic radiation having a frequency of 22 to 81GHz, and methods of mitigating dirt build-up on substrates.

BACKGROUND OF THE INVENTION

Recent advances have been made in technologies related to self-driving(“autonomous”) vehicles and other objects in a vehicle's surroundingsincluding markings that are detectable by a sensor mounted on theautonomous vehicle. Autonomous vehicles use a combination of detectingsystems, such as sensors, cameras, radar, ultrasonic, and lasers todetect and locate obstacles such that the autonomous vehicle can safelynavigate around such objects. Some detecting systems are limited intheir ability to detect objects at long distances or in non-idealenvironments, such as in inclement weather or due to build-up of dirtand other contaminants, including ice and water in the form of droplets,rivulets, or sheets on detecting system surfaces. Such limitations mayprohibit the autonomous vehicle from safely navigating obstacles. Easycleaning of coated surfaces is a significant selling point for theautonomous vehicle market, as well as many other industries, in bothconsumer and industrial markets.

Easy removal of dirt or other contaminants and prevention of contaminantbuild-up are desirable properties for products such as automobiles andautonomous vehicles. Environmental contaminants such as tar, asphalt,animal droppings, road salt, detergents, and the like may damage thesurface of coated vehicles, architectural surfaces, and other industrialsubstrates. Damage may be caused by a chemical reaction of thecontaminant with the coated surface such as by chemical etching, or mayinvolve physical removal of part or all of the coating from thesubstrate (i. e., “cohesive failure”) upon removal of the contaminantduring cleaning. Cohesive failure may also involve incomplete removal ofthe contaminant from the coated surface during cleaning.

The use of hydrophobic acrylates as additives has been the main approachto yield easy-to-clean (“E2C”) coatings such as automotive clearcoats.However, incompatibility of conventional film-forming binders, whichtend to be hydrophilic, and the hydrophobic additives limits theapplicability of this approach, because stratification of the materialsupon application to a substrate leads to irregular distribution of thehydrophobic additive as well as an undesirable increase of haze.Additionally, short duration of the contaminant mitigation properties ofcurrent E2C compositions, due to poor durability, has limited their use.

It would be desirable to provide coated articles demonstratingtransparency to electromagnetic radiation and methods of mitigatingcontaminant build-up on a substrate in order to overcome thedisadvantages of the prior art.

SUMMARY OF THE INVENTION

The present invention is directed to coated articles such as coatedvehicle components comprising:

(1) a substrate that is transparent to electromagnetic radiation havinga frequency of 22 to 81 GHz; and

(2) a curable film-forming composition applied to at least one surfaceof the substrate and cured thereon. The curable film-forming compositioncomprises:

(a) a first film-forming polymer prepared from at least one hydrophobicmonomer and having reactive functional groups, wherein the firstfilm-forming polymer (a) is present in the curable film-formingcomposition in an amount of 20 to 40 percent by weight, based on thetotal weight of resin solids in the curable film-forming composition;

(b) a second film-forming polymer different from the first film-formingpolymer (a) and prepared from at least one hydrophobic monomer, whereinthe second film-forming polymer (b) is present in the curablefilm-forming composition in an amount of 0.5 to 15 percent by weight,based on the total weight of resin solids in the curable film-formingcomposition; and

(c) a curing agent comprising functional groups reactive with thereactive functional groups in (a). Upon application of the curablefilm-forming composition to a substrate to form a coating layer, thefirst film-forming polymer (a) is distributed throughout the coatinglayer, and a concentration of the second film- forming polymer (b) isgreater within a surface region of the coating layer than aconcentration of the second film-forming polymer (b) within a bulkregion of the coating layer; and the coated article demonstrates atransmission of electromagnetic radiation having a frequency of 22 to 81GHz in the range of 70% to 100%.

The present invention is also drawn to methods of mitigating contaminantbuild-up on a substrate that is transparent to electromagnetic radiationhaving a frequency of 22 to 81 GHz, comprising applying one or morecoatings to at least a portion of the substrate to form a coatedsubstrate; and heating the coated substrate to a temperature and for atime sufficient to cure all the film-forming compositions. The outermostcoating layer comprises the curable film-forming composition describedabove.

DETAILED DESCRIPTION OF THE INVENTION

Other than in any operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients, reaction conditions and soforth used in the specification and claims are to be understood as beingmodified in all instances by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

As used in this specification and the appended claims, the articles “a,”“an,” and “the” include plural referents unless expressly andunequivocally limited to one referent.

The term “curable”, as used for example in connection with a curablecomposition, means that the indicated composition is polymerizable orcross linkable through functional groups, e.g., by means that include,but are not limited to, thermal (including ambient cure) and/orcatalytic exposure.

The term “cure”, “cured” or similar terms, as used in connection with acured or curable composition, e.g., a “cured composition” of somespecific description, means that at least a portion of the polymerizableand/or crosslinkable components that form the curable composition ispolymerized and/or crosslinked. Additionally, curing of a polymerizablecomposition refers to subjecting said composition to curing conditionssuch as but not limited to thermal curing, leading to the reaction ofthe reactive functional groups of the composition, and resulting inpolymerization and formation of a polymerizate. When a polymerizablecomposition is subjected to curing conditions, following polymerizationand after reaction of most of the reactive end groups occurs, the rateof reaction of the remaining unreacted reactive end groups becomesprogressively slower. The polymerizable composition can be subjected tocuring conditions until it is at least partially cured. The term “atleast partially cured” means subjecting the polymerizable composition tocuring conditions, wherein reaction of at least a portion, such as atleast 10 percent, or at least 20 percent, of the reactive groups of thecomposition occurs, to form a polymerizate. The polymerizablecomposition can also be subjected to curing conditions such that asubstantially complete cure is attained (such as at least 70 percent, orat least 80 percent, or at least 90 percent up to 100 percent, of thereactive groups react) and wherein further curing results in nosignificant further improvement in polymer properties, such as hardness.

The various embodiments and examples of the present invention aspresented herein are each understood to be non-limiting with respect tothe scope of the invention.

The first film-forming polymer (a) in the curable film-formingcomposition used to prepare the coated article of the present inventionis prepared from at least one hydrophobic monomer and has reactivefunctional groups. By “polymer” is meant a polymer includinghomopolymers and copolymers, and oligomers. By “hydrophobic” is meantthat the material described as such (e. g., a monomer or polymer) hasnon-polar properties and has a tendency to interact with, be misciblewith, or be dissolved by non-polar solvents such as alkanes and oils. Bydefinition, a molecule may be nonpolar either when there is an equalsharing of electrons between the two atoms of a diatomic molecule orbecause of the symmetrical arrangement of polar bonds in a more complexmolecule, such that there is no overall dipole in the molecule.

The first film-forming polymer is usually an acrylic polymer. Theacrylic polymer can be prepared from a reaction mixture comprising ahydrophobic monomer and a monomer having reactive functional groups.Examples of suitable hydrophobic monomers include ethylenicallyunsaturated monomers such as lauryl (meth)acrylate, stearyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, andthe like. The term “(meth)acrylate” is meant to encompass acrylateand/or methacrylate molecular structures where they exist. Note that thephrase “and/or” when used in a list is meant to encompass alternativeembodiments including each individual component in the list as well asany combination of components. For example, the list “A, B, and/or C” ismeant to encompass seven separate embodiments that include A, or B, orC, or A+B, or A+C, or B+C, or A+B+C.

The first film-forming polymer (a) often comprises an acrylic polymerprepared from a reaction mixture comprising a hydrophobic monomer,wherein the hydrophobic monomer comprises a fluorinated monomer and/or asiloxane. Suitable hydrophobic monomers comprising siloxane includeethylenically unsaturated monomers comprising polydialkylsiloxanefunctional groups, usually polydimethylsiloxane functional groups. Suchmonomers may be prepared, for example, by reacting a polydialkylsiloxanehaving hydroxyl end groups with an ethylenically unsaturated monomerthat has functional groups reactive with hydroxyl groups, such as acidor epoxy functional groups.

Examples of suitable ethylenically unsaturated monomers comprisingpolydialkylsiloxane functional groups include (meth)acrylate monomerssuch as X-22-2426 (available from Shin-Etsu Chemical Co), MCR-M07,MCR-M11, MCR-M17, MCR-M22, MCS-M11, MFR-M15 and MFS-M15 (available fromGelest, Inc), FM-0711, FM-0721 and FM-0725 (available from JNCCorporation).

The ethylenically unsaturated monomer comprising polydialkylsiloxanefunctional groups typically has a weight average molecular weight of1,000 to 30,000 Da, measured by GPC using polystyrene calibrationstandards, 2 PL gel MIXED-C as the column, THF as eluent at 1 ml/min andrefractive index detector. The polydialkylsiloxane group is typically atleast oligomeric, such that the resulting ethylenically unsaturatedmonomer is often a macromonomer.

The hydrophobic monomer may also (or alternatively) comprise afluorinated monomer. Nonlimiting examples of suitable ethylenicallyunsaturated monomers containing fluorine include fluoroethylene,chlorotrifluoroethylene, vinylidene fluoride, and hexafluoropropylene.Other fluorinated monomers include2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluoroheptyl (meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Heneicosafluorododecyl(meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyl(meth)acrylate, 2,2,3,3,4,4,4-Heptafluorobutyl (meth)acrylate,2,2,3,4,4,4-Hexafluorobutyl (meth)acrylate,1,1,1,3,3,3-Hexafluoroisopropyl (meth)acrylate,2,2,3,3,4,4,5,5-Octafluoropentyl (meth)acrylate,2,2,3,3,3-Pentafluoropropyl (meth)acrylate, 1 H,1 H,2H,2H-Perfluorodecyl(meth)acrylate, 2,2,3,3-Tetrafluoropropyl (meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl (meth)acrylate,2,2,2-Trifluoroethyl (meth)acrylate, and2-[(1′,1′,1′,V-Trifluoro-2′-(trifluoromethyl)-2′-hydroxy)propyl]-3-norbornyl(meth)acrylate.

The first film-forming polymer has reactive functional groups. The term“reactive” refers to a functional group capable of undergoing a chemicalreaction with itself and/or other functional groups spontaneously orupon the application of heat or in the presence of a catalyst or by anyother means known to those skilled in the art. The functional groups onthe first film-forming binder may be selected from at least one ofcarboxylic acid groups, amine groups, epoxide groups, hydroxyl groups,thiol groups, carbamate groups, amide groups, urea groups,(meth)acrylate groups, styrenic groups, vinyl groups, allyl groups,aldehyde groups, acetoacetate groups, hydrazide groups, cycliccarbonate, acrylate, maleic and mercaptan groups. The functional groupson the film-forming polymer are often selected so as to be reactive withthose on the curing agent (c). The reactive functional groups on thefirst film-forming polymer are usually active hydrogen groups such ashydroxyl, carboxyl, carbamate, primary and/or secondary amine, amide,thiol, and the like as known to those skilled in the art.

Useful hydroxyl functional ethylenically unsaturated monomers includehydroxyalkyl (meth)acrylates, typically having 2 to 4 carbon atoms inthe hydroxyalkyl group, such as hydroxyethyl (meth)acrylate,hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, hydroxyfunctional adducts of caprolactone and hydroxyalkyl (meth)acrylates, aswell as the beta-hydroxy ester functional monomers described below.

Beta-hydroxy ester functional monomers can be prepared fromethylenically unsaturated, epoxy functional monomers and carboxylicacids having from about 13 to about 20 carbon atoms, or fromethylenically unsaturated acid functional monomers and epoxy compoundscontaining at least 5 carbon atoms which are not polymerizable with theethylenically unsaturated acid functional monomer.

Useful ethylenically unsaturated, epoxy functional monomers used toprepare the beta-hydroxy ester functional monomers include, but are notlimited to, glycidyl (meth)acrylate, allyl glycidyl ether, methallylglycidyl ether, 1:1 (molar) adducts of ethylenically unsaturatedmonoisocyanates with hydroxy functional monoepoxides such as glycidol,and glycidyl esters of polymerizable polycarboxylic acids such as maleicacid. Glycidyl (meth)acrylate is preferred. Examples of carboxylic acidsinclude, but are not limited to, saturated monocarboxylic acids such asisostearic acid and aromatic unsaturated carboxylic acids.

Useful ethylenically unsaturated acid functional monomers used toprepare the beta-hydroxy ester functional monomers includemonocarboxylic acids such as acrylic acid, methacrylic acid, crotonicacid; dicarboxylic acids such as itaconic acid, maleic acid and fumaricacid; and monoesters of dicarboxylic acids such as monobutyl maleate andmonobutyl itaconate. (Note that these acid functional monomers may alsobe used in the reaction mixture to prepare the first film-formingpolymer, providing acid functional reactive groups thereto.) Theethylenically unsaturated acid functional monomer and epoxy compound aretypically reacted in a 1:1 equivalent ratio. The epoxy compound does notcontain ethylenic unsaturation that would participate in freeradical-initiated polymerization with the unsaturated acid functionalmonomer. Useful epoxy compounds include 1,2-pentene oxide, styrene oxideand glycidyl esters or ethers, usually containing from 7 to 30 carbonatoms, such as butyl glycidyl ether, octyl glycidyl ether, phenylglycidyl ether and para-(tertiary butyl) phenyl glycidyl ether. Commonlyused glycidyl esters include those of the structure:

where R is a hydrocarbon radical containing from about 4 to about 26carbon atoms. Preferably, R is a branched hydrocarbon group having fromabout 8 to about 10 carbon atoms, such as neopentyl, neoheptanyl orneodecanyl. Suitable glycidyl esters of carboxylic acids includeVERSATIC ACID 911 and CARDURA E, each of which is commercially availablefrom Shell Chemical Co.

Carbamate functional groups can be included in the acrylic polymer bycopolymerizing the acrylic monomers with a carbamate functional vinylmonomer, such as a carbamate functional alkyl ester of methacrylic acid,or by reacting a hydroxyl functional acrylic polymer with a lowmolecular weight carbamate functional material, such as can be derivedfrom an alcohol or glycol ether, via a transcarbamoylation reaction. Inthis reaction, a low molecular weight carbamate functional materialderived from an alcohol or glycol ether is reacted with the hydroxylgroups of the acrylic polyol, yielding a carbamate functional acrylicpolymer and the original alcohol or glycol ether. The low molecularweight carbamate functional material derived from an alcohol or glycolether may be prepared by reacting the alcohol or glycol ether with ureain the presence of a catalyst. Suitable alcohols include loweraliphatic, cycloaliphatic, and aromatic alcohols (i. e., usually havingeight or less carbon atoms) such as methanol, ethanol, propanol,butanol, cyclohexanol, 2-ethylhexanol, and 3-methylbutanol. Suitableglycol ethers include ethylene glycol methyl ether and propylene glycolmethyl ether. Propylene glycol methyl ether and methanol are most oftenused. Other carbamate functional monomers as known to those skilled inthe art may also be used.

Amide functionality may be introduced to the acrylic polymer by usingsuitably functional monomers in the preparation of the polymer, or byconverting other functional groups to amido-groups using techniquesknown to those skilled in the art. Likewise, other functional groups maybe incorporated as desired using suitably functional monomers ifavailable or conversion reactions as necessary.

The ethylenically unsaturated monomer comprising reactive functionalgroups is typically present in the reaction mixture that may be used toprepare the first film-forming polymer in an amount of 1 to 30, such as1 to 20, or 1 to 10 percent by weight, based on the total weight ofmonomers in the reaction mixture.

One or more other polymerizable ethylenically unsaturated monomers maybe included in the reaction mixture that may be used to prepare thefirst film-forming polymer. Useful alkyl esters of acrylic acid ormethacrylic acid include aliphatic alkyl esters containing from 1 to 30,and preferably 4 to 18 carbon atoms in the alkyl group. Non-limitingexamples include methyl (meth)acrylate, ethyl (meth)acrylate, and butyl(meth)acrylate. Suitable other copolymerizable ethylenically unsaturatedmonomers include vinyl aromatic compounds such as styrene and vinyltoluene; nitriles such as acrylonitrile and methacrylonitrile; vinyl andvinylidene halides such as vinyl chloride and vinylidene fluoride andvinyl esters such as vinyl acetate. Styrene is often used.

When used, these additional ethylenically unsaturated monomers aretypically present in the reaction mixture used to prepare the acrylicpolymer in an amount of 5 to 50, more often 10 to 30 percent by weight,based on the total weight of monomers in the reaction mixture.

The first film-forming polymer (a) may be prepared using known additionpolymerization techniques, such as organic solution polymerizationtechniques, in particular from the afore-mentioned reaction mixtures.Exemplary methods are illustrated in the examples below.

The curable film-forming compositions used to prepare the coatedarticles of the present invention further comprise (b) a secondfilm-forming polymer prepared from at least one hydrophobic monomer. Thesecond film-forming polymer may be prepared from any of the monomerslisted above used to prepare the first film-forming polymer. The secondfilm-forming polymer may also have reactive functional groups such asany of those described above. In a particular example of the presentinvention, the second film-forming polymer (b) comprises an acrylicpolymer prepared from a reaction mixture comprising a hydrophobicmonomer and a monomer having a functional group reactive with thefunctional groups on the curing agent (c), wherein the hydrophobicmonomer comprises a fluorinated monomer and/or a siloxane. However, thesecond film-forming polymer (b) is different from the first film-formingpolymer (a). Each is prepared using monomers such that upon applicationof the curable film-forming composition to a substrate to form a coatinglayer, the first film-forming polymer is distributed throughout thecoating layer with respect to a cross-section of the coating layer. Thatis, the concentration of the first film-forming polymer with respect tothe entire coating composition is substantially consistent throughoutthe coating layer. Additionally, the concentration of the secondfilm-forming polymer is greater at the surface region of the coatinglayer than the concentration of the second film-forming polymer withinthe bulk region of the coating layer. By “surface region” is meant theoutermost 10% of the coating layer thickness after the coatingcomposition is applied to a substrate. By “bulk region” is meant theremainder of the coating layer thickness under the surface region. Forexample, in a coating layer having a dry film thickness (DFT) of 100microns after curing, the surface region is the outermost 10 microns ofthe coating layer. Thus the mass ratio of the second film-formingpolymer to the first film-forming polymer is greater in the surfaceregion of the coating layer than in the bulk of the coating layer. Thesedistribution phenomena of the two polymers may be attained by preparingthe respective film-forming polymers so that the second film-formingpolymer (b) is more hydrophobic than the first film-forming polymer (a).This may be accomplished by using a higher amount of hydrophobicmonomers in the preparation of the second film-forming polymer than inthe first film-forming polymer. For example, in the preparation of thefirst film-forming polymer (a), the hydrophobic monomer is typicallypresent in the reaction mixture in an amount of 4 to 15 percent byweight, such as 5 to 13 percent by weight, based on the total weight ofmonomers in the reaction mixture. In contrast, in the preparation of thesecond film-forming polymer (b), the hydrophobic monomer is typicallypresent in the reaction mixture in an amount of 15 to 60 percent byweight, such as 20 to 50 percent by weight or 20 to 40 percent byweight, based on the total weight of monomers in the reaction mixture.

In addition, the amount of each polymer in the curable film-formingcomposition is different. Typically the first film-forming polymer (a)is present in the curable film-forming composition in an amount of atleast 20 percent by weight, or at least 25 percent by weight, or atleast 30 percent by weight, and at most 40 percent by weight, or at most35 percent by weight, based on the total weight of resin solids in thecurable film-forming composition. The second film-forming polymer (b) ispresent in the curable film-forming composition in an amount of at least0.5 percent by weight, such as at least 1 percent by weight, and at most15 percent by weight, or at most 10 percent by weight, based on thetotal weight of resin solids in the curable film-forming composition.While not intending to be bound by theory, it is believed that thedistributions of the first and second film-forming polymers in a coatinglayer allow for an extended duration of dirt mitigation properties ofthe coating layer compared to coating layers that do not have such adistribution of polymers of varying hydrophobicity.

The curable film-forming compositions further comprise (c) a curingagent comprising functional groups that are reactive with the reactivefunctional groups in the polymer (a) and with the reactive functionalgroups in the polymer (b) when they are present.

The curing agent (c) used in the curable film-forming composition may beselected from one or more polyisocyanates such as diisocyanates andtriisocyanates including biurets and isocyanurates. Diisocyanatesinclude toluene diisocyanate, 4,4′-methylene-bis(cyclohexyl isocyanate),isophorone diisocyanate, an isomeric mixture of 2,2,4- and2,4,4-trimethyl hexamethylene diisocyanate, 1,6-hexamethylenediisocyanate, tetramethyl xylylene diisocyanate and/or4,4′-diphenylmethylene diisocyanate. Biurets of any suitablediisocyanate including 1,4-tetramethylene diisocyanate and1,6-hexamethylene diisocyanate may be used. Also, biurets ofcycloaliphatic diisocyanates such as isophorone diisocyanate and4,4′-methylene-bis-(cyclohexyl isocyanate) can be employed. Examples ofsuitable aralkyl diisocyanates from which biurets may be prepared aremeta-xylylene diisocyanate and α,α,α′,α′-tetramethylmeta-xylylenediisocyanate.

Trifunctional isocyanates may also be used as the curing agent, forexample, trimers of isophorone diisocyanate, triisocyanato nonane,triphenylmethane triisocyanate, 1,3,5-benzene triisocyanate,2,4,6-toluene triisocyanate, an adduct of trimethylol and tetramethylxylene diisocyanate sold under the name CYTHANE 3160 by CYTECIndustries, and DESMODUR N 3390, which is the isocyanurate ofhexamethylene diisocyanate, available from Bayer Corporation.Specifically used polyisocyanates are trimers of diisocyanates such ashexamethylene diisocyanate and isophorone diisocyanate. Desmodur Z 4470BA, an aliphatic polyisocyanate based on isophorone diisocyanateavailable from Bayer Corporation, is also suitable.

The polyisocyanate may also be one of those disclosed above, chainextended with one or more polyamines and/or polyols using suitablematerials and techniques known to those skilled in the art to form apolyurethane prepolymer having isocyanate functional groups.

Mixtures of aliphatic polyisocyanates are particularly suitable.

The curing agent (c) used in the curable film-forming composition mayalternatively or additionally be selected from one or more aminoplastresins. Useful aminoplast resins are based on the addition products offormaldehyde with an amino- or amido-group carrying substance.Condensation products obtained from the reaction of alcohols andformaldehyde with melamine, urea or benzoguanamine are most common andpreferred herein. While the aldehyde employed is most oftenformaldehyde, other similar condensation products can be made from otheraldehydes, such as acetaldehyde, crotonaldehyde, acrolein, benzaldehyde,furfural, glyoxal and the like.

Condensation products of other amines and amides can also be used, forexample, aldehyde condensates of triazines, diazines, triazoles,guanadines, guanamines and alkyl- and aryl-substituted derivatives ofsuch compounds, including alkyl- and aryl-substituted ureas and alkyl-and aryl-substituted melamines. Non-limiting examples of such compoundsinclude N,N′-dimethyl urea, benzourea, dicyandiamide, formaguanamine,acetoguanamine, glycoluril, ammeline, 3,5-diaminotriazole,triaminopyrimidine, 2-mercapto-4,6-diaminopyrimidine and carbamoyltriazines of the formula C₃N₃(NHCOXR)₃ where X is nitrogen, oxygen orcarbon and R is a lower alkyl group having from one to twelve carbonatoms or mixtures of lower alkyl groups, such as methyl, ethyl, propyl,butyl, n-octyl and 2-ethylhexyl. Such compounds and their preparationare described in detail in U.S. Pat. No. 5,084,541.

The aminoplast resins often contain methylol or similar alkylol groups,and in most instances at least a portion of these alkylol groups areetherified by reaction with an alcohol. Any monohydric alcohol can beemployed for this purpose, including methanol, ethanol, propanol,butanol, pentanol, hexanol, heptanol, as well as benzyl alcohol andother aromatic alcohols, cyclic alcohols such as cyclohexanol,monoethers of glycols, and halogen-substituted or other substitutedalcohols such as 3-chloropropanol and butoxyethanol. Many aminoplastresins are partially alkylated with methanol or butanol.

The curing agent (c) is typically present in the film-formingcompositions in an amount ranging from 30 to 79.5 percent by weight,such as 40 to 65 percent by weight, often 45 to 60 percent by weight,based on the total weight of resin solids in the composition.

The curable film-forming composition used to prepare the coated articlesof the present invention may further comprise (d) an additionalfilm-forming resin component that is i) different from the first andsecond film-forming polymers (a) and (b); and ii) has functional groupsthat are reactive with at least one other component of the curablefilm-forming composition. Such a component (d) may comprise one or morefilm-forming polymers and/or curing agents.

The additional film-forming resin component (d) may comprise an addition(such as an acrylic) polymer, polyester polymer, polyurethane polymer,polyether polymer, polyester acrylate, and/or polyurethane acrylate.Often an acrylic polymer and/or polyester polymer having multiplehydroxyl functional groups is used.

Suitable acrylic polymers include copolymers of one or more monomerssuch as any of those disclosed above.

A polyester polymer may also be used in the additional film-formingresin component (d). Such polymers may be prepared in a known manner bycondensation of polyhydric alcohols and polycarboxylic acids. Suitablepolyhydric alcohols include, but are not limited to, ethylene glycol,propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentylglycol, diethylene glycol, glycerol, trimethylol propane, andpentaerythritol. Suitable polycarboxylic acids include, but are notlimited to, succinic acid, adipic acid, azelaic acid, sebacic acid,maleic acid, fumaric acid, phthalic acid, tetrahydrophthalic acid,hexahydrophthalic acid, and trimellitic acid. Besides the polycarboxylicacids mentioned above, functional equivalents of the acids such asanhydrides where they exist or lower alkyl esters of the acids such asthe methyl esters may be used. Polyesters derived from cyclic esterssuch as caprolactone are also suitable. Polyester acrylates, such asacrylic polymers having polyester side chains, may also be used.

Polyurethanes can also be used in the additional film-forming resincomponent (d). Among the polyurethanes which can be used are polymericpolyols which generally are prepared by reacting the polyester polyolsor acrylic polyols such as those mentioned above with a polyisocyanatesuch that the OH/NCO equivalent ratio is greater than 1:1 so that freehydroxyl groups are present in the product. The organic polyisocyanatewhich is used to prepare the polyurethane polyol can be an aliphatic oran aromatic polyisocyanate or a mixture of the two. Any of thosedisclosed above may be used in the preparation of the polyurethane.Polyurethane acrylates, such as acrylic polymers having polyurethaneside chains, may also be used.

Examples of polyether polyols are polyalkylene ether polyols whichinclude those having the following structural formula:

where the substituent R₁ is hydrogen or lower alkyl containing from 1 to5 carbon atoms including mixed substituents, and n is typically from 2to 6 and m is from 8 to 100 or higher. Included arepoly(oxytetramethylene) glycols, poly(oxyethylene) glycols,poly(oxy-1,2-propylene) glycols, and poly(oxy-1,2-butylene) glycols.

Also useful are polyether polyols formed from oxyalkylation of variouspolyols, for example, diols such as ethylene glycol, 1,6-hexanediol,Bisphenol A and the like, or other higher polyols such astrimethylolpropane, pentaerythritol, and the like. Polyols of higherfunctionality which can be utilized as indicated can be made, forinstance, by oxyalkylation of compounds such as sucrose or sorbitol. Onecommonly utilized oxyalkylation method is reaction of a polyol with analkylene oxide, for example, propylene or ethylene oxide, in thepresence of an acidic or basic catalyst. Particular polyethers includethose sold under the names TERATHANE and TERACOL, available from E. I.Du Pont de Nemours and Company, Inc., and POLYMEG, available from Q OChemicals, Inc., a subsidiary of Great Lakes Chemical Corp.

Useful amine functional film-forming polymers include polyoxypropyleneamines such as those commercially available under the trademarkdesignation JEFFAMINE®; amine functional acrylic polymers and polyesterpolymers prepared as known in the art are also suitable.

The additional film-forming resin component (d) may include anaminoplast such as any of those disclosed above. In a particular exampleof the present invention, the additional film-forming resin component(d) comprises an acrylic and/or polyester polyol and an aminoplast.

When used, the additional film-forming resin component (d) is typicallypresent in the film-forming compositions in an amount ranging from 30 to49.5 percent by weight, often 35 to 45 percent by weight, based on thetotal weight of resin solids in the composition.

In certain examples of the present invention, the curable film-formingcomposition further comprises (d′) a saturated fatty acid such ascaprylic acid, capric acid, lauric acid, myristic acid, palmitic acid,stearic acid, arachidic acid, behenic acid, lignoceric acid, and ceroticacid; and (e) a tin-containing catalyst such as triphenyl tin hydroxide,butyl stannoic acid, dioctyltin oxide, dibutyltin dilaurate, dibutyltindiacetate, and dibutyltin oxide. Curable film-forming compositionscontaining fatty acids and tin-containing catalysts are particularlysuitable for use on plastic substrates that require lower curetemperatures to avoid deformation.

The curable film-forming composition can additionally include a varietyof optional ingredients and/or additives that are somewhat dependent onthe particular application of the curable composition, such as othercuring catalysts, pigments or other colorants, reinforcements,thixotropes, accelerators, surfactants, plasticizers, extenders,stabilizers, corrosion inhibitors, diluents, hindered amine lightstabilizers, UV light absorbers, adhesion promoters, and antioxidants.The curable film-forming composition may be a color coat or clear coat;it may be opaque (less than 10% visible light transmittance),translucent (10 to 70% visible light transmittance), tinted transparent,or colorless transparent. The term “transparent”, as used in connectionwith a clear coat, means that the indicated coating has the property oftransmitting visible light without appreciable scattering so thatobjects lying beyond are entirely visible. As used herein, transparentclear coats demonstrate a visible light transmittance (% Transmission,as defined by the equation in the Examples below using visible light) ofat least 70%. Additionally, the curable film-forming compositions usedto prepare the coated articles of the present invention are transparentto electromagnetic radiation used in signaling devices such astransmitters and receivers for autonomous vehicles, including both shortrange and long range frequencies. For example, the curable film-formingcompositions are typically transparent (i.e., demonstrate a %Transmission of at least 70) to electromagnetic radiation having anyfrequency between 22 and 81 GHz, in particular, 76 to 81 GHz.

The curable compositions used in the present invention can be preparedas a two-package composition, often curable at ambient temperature. By“ambient” conditions is meant without the application of heat or otherenergy; for example, when a curable composition undergoes athermosetting reaction without baking in an oven, use of forced air,irradiation, or the like to prompt the reaction, the reaction is said tooccur under ambient conditions. Usually ambient temperature ranges from60 to 90° F. (15.6 to 32.2° C.), such as a typical room temperature, 72°F. (22.2° C.). Two-package curable compositions are typically preparedby combining the ingredients immediately before use. The curablefilm-forming compositions may alternatively be prepared as one-packagesystems.

To prepare the coated articles of the present invention, the curablefilm- forming composition described above may be applied to at least onesurface of a substrate.

Suitable substrates include any that are transparent (i. e., demonstratea light transmittance (% Transmission, as defined in the Examples below)of at least 70%) to electromagnetic radiation having any frequencybetween 22 and 81 GHz, in particular, 76 to 81 GHz. For example, thecurable film-forming compositions may be applied over optical substratesknown in the art, including non-plastic substrates such as glass.Suitable examples of optical plastic substrates include polyol(allylcarbonate), e.g., allyl diglycol carbonates such as diethylene glycolbis(allyl carbonate), which is sold under the trademark CR-39 by PPG;polyurea-polyurethane (polyurea urethane) polymers, which are prepared,for example, by the reaction of a polyurethane prepolymer and a diaminecuring agent, a composition for one such polymer being sold under thetrademark TRIVEX® by PPG; polyol(meth)acryloyl terminated carbonatemonomer; diethylene glycol dimethacrylate monomers; ethoxylated phenolmethacrylate monomers; diisopropenyl benzene monomers; ethoxylatedtrimethylol propane triacrylate monomers; ethylene glycolbismethacrylate monomers; poly(ethylene glycol) bismethacrylatemonomers; urethane acrylate monomers; poly(ethoxylated Bisphenol Adimethacrylate); poly(vinyl acetate); poly(vinyl alcohol); poly(vinylchloride); poly(vinylidene chloride); polyethylene; polypropylene;polyurethanes; polythiourethanes; thermoplastic polycarbonates, such asthe carbonate-linked resin derived from Bisphenol A and phosgene, onesuch material being sold under the trademark LEXAN; polyesters, such asthe material sold under the trademark MYLAR; poly(ethyleneterephthalate); polyvinyl butyral; poly(methyl methacrylate), such asthe material sold under the trademark PLEXIGLAS, and polymers preparedby reacting polyfunctional isocyanates with polythiols or polyepisulfidemonomers, either homopolymerized or co-and/or terpolymerized withpolythiols, polyisocyanates, polyisothiocyanates and optionallyethylenically unsaturated monomers or halogenated aromatic-containingvinyl monomers. Also suitable are copolymers of such monomers and blendsof the described polymers and copolymers with other polymers, e.g., toform interpenetrating network products. Such optical substrates may beused as lenses, screens, or covers (for transmitters, receivers, and thelike) on components of autonomous vehicles.

The curable film-forming compositions may also be applied overelastomeric, plastic, or composite substrates such as those that arefound on motor vehicles and used as vehicle components such as wheels,bumpers, fenders, hoods, doors, panels, etc. These vehicle parts may beformed from any of the common thermoplastic or thermosetting syntheticmaterials, including thermoplastic olefins such as polyethylene andpolypropylene, thermoplastic urethane, polycarbonate, thermosettingsheet molding compound, reaction-injection molding compound,acrylonitrile-based materials, nylon, and the like. By “composite” ismeant any substrate made of fibers, typically of glass or carbon, orother filler material that is incorporated with polymeric or plasticmaterials, commonly of epoxy type polymers.

Before depositing any coating compositions upon the surface of thesubstrate, it is common practice, though not necessary, to removeforeign matter from the surface by thoroughly cleaning and degreasingthe surface. Such cleaning typically takes place after forming thesubstrate (molding, etc.) into an end-use shape. The surface of thesubstrate can be cleaned by physical and/or chemical means, such asmechanically abrading the surface or cleaning/degreasing withcommercially available cleaning agents which are well known to thoseskilled in the art.

Following the cleaning step, the substrate may be rinsed with deionizedwater, with a solvent, or an aqueous solution of rinsing agents in orderto remove any residue. The substrate can be air dried, for example, byusing an air knife, by flashing off the water by brief exposure of thesubstrate to a higher temperature or by passing the substrate betweensqueegee rolls.

The substrate may be a bare, cleaned surface; it may be oily, pretreatedwith one or more pretreatment or adhesion promoting compositions, and/orprepainted with one or more coating compositions, primers, topcoats,etc., applied by any method including, but not limited to, spraying, dipcoating, roll coating, curtain coating, and the like.

The compositions may be applied to the substrate by one or more of anumber of methods including spraying, dipping/immersion, brushing, orflow coating, but they are most often applied by spraying. The usualspray techniques and equipment for air spraying and electrostaticspraying and either manual or automatic methods can be used. The coatinglayer typically has a dry film thickness of 1-25 mils (25.4-635microns), often 5-25 mils (127-635 microns).

The film-forming compositions can be applied directly to the surface ofa substrate or onto an adhesion promoter layer, primer coat or othercoating as noted above, such as a topcoat, on the substrate to form acoated substrate in accordance with the present invention.Alternatively, a primer may not be used and the film-formingcompositions can be applied directly to an adhesion promoter, apigmented basecoat or other coating. Multiple coating layers such as aprimer and optionally a colored base coat may be applied to thesubstrate prior to application of the curable film-forming compositionof the present invention. Thus, the coated article of the presentinvention may comprise: A) a pigmented, curable film-forming compositionapplied to at least one surface of the substrate to form a base coatedsubstrate, and B) a transparent, curable film-forming compositionapplied to at least one surface of the base coated substrate, whereinthe transparent, curable film-forming composition is prepared from thecurable film-forming composition described above.

After forming a film of the coating on the substrate, the compositioncan be cured by heating to a temperature and for a time sufficient tocure the composition; for example, by allowing it to stand at ambienttemperature (such as a typical room temperature, 72° F. (22.2° C.)), ora combination of ambient temperature cure and baking, or by bakingalone. The composition may be cured at ambient temperature typically ina period ranging from about 24 hours to about 36 hours. If ambienttemperature and baking are utilized in combination, the composition isoften allowed to stand (“flash”) for a period of from about 2 minutes toabout 120 minutes at a temperature ranging from ambient to 175° F.(79.4° C.), followed by baking at a temperature up to about 300° F.(148.9° C.), usually 285° F. (140.6° C.) for a period of time rangingfrom about 20 minutes to about 1 hour. For plastic substrates that areheat-sensitive and may deform at high temperatures, the curablefilm-forming compositions may be curable at temperatures lower than 90°C.

After application of the curable film-forming composition to thesubstrate and upon curing, the coated article demonstrates atransmission of electromagnetic radiation having any frequency between22 and 81 GHz in the range of 70% to 100%, such as 75% to 100%, or 80%to 100% measured as demonstrated in the Examples below. The coatedarticle of the present invention additionally demonstrates contaminantmitigation properties as evidenced by radar transmission when subjectedto various tests described in the Examples below. Such properties renderthe curable film-forming compositions of the present inventionparticularly suitable for use in methods of mitigating contaminantbuild-up on a substrate, in accordance with the present invention.

In the method of the present invention, contaminant build-up on asubstrate is mitigated by applying to at least a portion of thesubstrate the curable film-forming composition described above and thenat least partially curing the curable film-forming composition. Acurable film-forming composition is applied to at least one surface ofthe substrate. A substrate may have one continuous surface, or two ormore surfaces such as two opposing surfaces. Typically the surface thatis coated is any that is expected to be exposed to conditions conduciveto dirt build-up, such as consumer and industrial vehicles and buildingstructures. By “dirt” is meant soil, grease, oil, minerals, detergent,salt, tar, asphalt, animal droppings, insects (“bug splatter”), treesap, and the like; contaminants that are commonly found outside or inindustrial settings, and that tend to adhere to vehicle surfaces. Othercontaminants include water and ice. Water in the form of droplets,rivulets, or sheets, and ice on the surface of a substrate may impedethe transmission of a signal through the substrate. In a particularexample of the present invention, a method of mitigating contaminantbuild up on a substrate is provided, comprising:

(1) applying a first coating comprising a pigmented, curablefilm-forming composition to at least a portion of the substrate to forma base coated substrate;

(2) applying a transparent, curable film-forming composition to at leasta portion of the base coated substrate formed in step (1) prior tosubstantially curing the first coating to form a multi-layer coatedsubstrate, wherein the transparent, curable film-forming composition isprepared from the curable film-forming compositions described above; and

(3) heating the multi-layer coated substrate formed in step (2) to atemperature and for a time sufficient to cure all the film-formingcompositions.

The methods of the present invention are particularly suitable for themitigation of contaminant build up on a component of a vehicle. Suchvehicles may include landcraft such as cars, trucks, sport utilityvehicles, motorcycles; watercraft such as boats, ships and submarines;aircraft such as airplanes and helicopters; construction vehicles; andmilitary vehicles, for example tanks and Humvees.

The methods of the present invention are particularly suitable for themitigation of contaminant build up on a component of an autonomousvehicle. Many vehicles in use today, including autonomous vehicles,utilize transmitters and sensors to send and receive signals for variouspurposes. It is vital for the continued accurate and safe operation ofsuch vehicles that these signals, which are typically electromagneticradiation in the form of radio waves, do not get impeded in any way.Coated substrates covering the transmitters and sensors must allow fortransmission of the signals therethrough. Mitigating contaminant buildup by using the methods of the present invention is particularlybeneficial.

Each of the embodiments and characteristics described above, andcombinations thereof, may be said to be encompassed by the presentinvention. For example, the present invention is thus drawn to thefollowing nonlimiting aspects:

In a first aspect, a coated article comprising:

-   -   (1) a substrate that is transparent to electromagnetic radiation        having a frequency of 22 to 81 GHz; and    -   (2) a curable film-forming composition applied to at least one        surface of the substrate and cured thereon, the curable        film-forming composition comprising:    -   (a) a first film-forming polymer having reactive functional        groups and prepared from a reaction mixture which comprises at        least one hydrophobic monomer present in the reaction mixture in        an amount of 4 to 15 percent by weight, based on the total        weight of monomers in the reaction mixture, wherein the first        film-forming polymer (a) is present in the curable film-forming        composition in an amount of 20 to 40 percent by weight, based on        the total weight of resin solids in the curable film-forming        composition;    -   (b) a second film-forming polymer different from the first        film-forming polymer (a) and prepared from a reaction mixture        which comprises at least one hydrophobic monomer comprising a        siloxane, wherein the hydrophobic monomer in the reaction        mixture used to prepare the second film-forming polymer (b) is        present in the reaction mixture in an amount of 15 percent by        weight to 60 percent by weight, based on the total weight of        monomers in the reaction mixture, and wherein the second        film-forming polymer (b) is present in the curable film-forming        composition in an amount of 0.5 to 15 percent by weight, based        on the total weight of resin solids in the curable film-forming        composition; and    -   (c) a curing agent comprising functional groups reactive with        the reactive functional groups in (a); wherein the second        film-forming polymer (b) is more hydrophobic than the first        film-forming polymer (a) and wherein upon application of the        curable film-forming composition to the substrate to form a        coating layer, the first film-forming polymer (a) is distributed        throughout the coating layer, and a concentration of the second        film-forming polymer (b) is greater within a surface region of        the coating layer than a concentration of the second        film-forming polymer (b) within a bulk region of the coating        layer; and wherein the coated article demonstrates a        transmission of electromagnetic radiation having a frequency of        22 to 81 GHz in the range of 70% to 100%.

In a second aspect, the coated article of the first aspect, wherein thehydrophobic monomer in the reaction mixture used to prepare the firstfilm-forming polymer (a) is selected from at least one of a siloxane,2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluoroheptyl(meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Heneicosafluorododecyl(meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyl(meth)acrylate, 2,2,3,3,4,4,4-Heptafluorobutyl (meth)acrylate,2,2,3,4,4,4-Hexafluorobutyl (meth)acrylate,1,1,1,3,3,3-Hexafluoroisopropyl (meth)acrylate,2,2,3,3,4,4,5,5-Octafluoropentyl (meth)acrylate,2,2,3,3,3-Pentafluoropropyl (meth)acrylate, 1H,1H,2H,2H-Perfluorodecyl(meth)acrylate, 2,2,3,3-Tetrafluoropropyl (meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl (meth)acrylate,2,2,2-Trifluoroethyl (meth)acrylate, and2-[(1′,1′,1′-Trifluoro-2′-(trifluoromethyl)-2′-hydroxy)propyl]-3-norbornyl(meth)acrylate.

In a third aspect, the coated article of any of the preceding aspects,wherein the reaction mixture used to prepare the second film-formingpolymer (b) further comprises a monomer having a functional groupreactive with the functional groups on the curing agent (c).

In a fourth aspect, the coated article of any of the preceding aspects,wherein the curing agent (c) comprises a polyisocyanate.

In a fifth aspect, the coated article of any of the preceding aspects,wherein the curable film-forming composition further comprises (d) anadditional film-forming resin component that (i) is different from thefirst and second film-forming polymers (a) and (b); and (ii) hasfunctional groups that are reactive with at least one other component ofthe curable film-forming composition.

In a sixth aspect, the coated article of the fifth aspect, wherein theadditional film-forming resin component (d) comprises an acrylic and/orpolyester polyol and an aminoplast.

In a seventh aspect, the coated article of any of the preceding aspects,wherein the curable film-forming composition is transparent to visiblelight.

In an eighth aspect, the coated article of any of the preceding aspects,wherein the substrate comprises plastic and the curable film-formingcomposition further comprises (d′) a saturated fatty acid and (e) a tincatalyst.

In a ninth aspect, the coated article of any of the preceding aspects,wherein the substrate comprises a component of a vehicle.

In a tenth aspect, the coated article of the ninth aspect, wherein thevehicle comprises an autonomous vehicle.

In an eleventh aspect, the coated article of any of the precedingaspects, wherein the reaction mixture used to prepare the secondfilm-forming polymer (b) further comprises a monomer having a functionalgroup reactive with the functional groups on the curing agent (c).

In a twelfth aspect, a coated vehicle component comprising:

(1) a substrate that is transparent to electromagnetic radiation havinga frequency of 22 to 81 GHz; and

(2) a curable film-forming composition applied to at least one surfaceof the substrate and cured thereon, the curable film-forming compositioncomprising:

(a) a first film-forming polymer prepared from at least one hydrophobicmonomer and having reactive functional groups, present in the reactionmixture in an amount of 4 to 15 percent by weight, based on the totalweight of monomers in the reaction mixture, and selected from at leastone of a siloxane,2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluoroheptyl(meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Heneicosafluorododecyl(meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyl(meth)acrylate, 2,2,3,3,4,4,4-Heptafluorobutyl (meth)acrylate,2,2,3,4,4,4-Hexafluorobutyl (meth)acrylate,1,1,1,3,3,3-Hexafluoroisopropyl (meth)acrylate,2,2,3,3,4,4,5,5-Octafluoropentyl (meth)acrylate,2,2,3,3,3-Pentafluoropropyl (meth)acrylate, 1H,1H,2H,2H-Perfluorodecyl(meth)acrylate, 2,2,3,3-Tetrafluoropropyl (meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl (meth)acrylate,2,2,2-Trifluoroethyl (meth)acrylate, and2-[(1′,1′,1′-Trifluoro-2′-(trifluoromethyl)-2′-hydroxy)propyl]-3-norbornyl(meth)acrylate; wherein the first film-forming polymer (a) is present inthe curable film-forming composition in an amount of 20 to 40 percent byweight, based on the total weight of resin solids in the curablefilm-forming composition;

(b) a second film-forming polymer different from the first film-formingpolymer (a) and prepared from a reaction mixture which comprises atleast one hydrophobic monomer comprising a siloxane, wherein thehydrophobic monomer in the reaction mixture used to prepare the secondfilm-forming polymer (b) is present in the reaction mixture in an amountof 15 percent by weight to 60 percent by weight, based on the totalweight of monomers in the reaction mixture, and wherein the secondfilm-forming polymer (b) is present in the curable film-formingcomposition in an amount of 0.5 to 15 percent by weight, based on thetotal weight of resin solids in the curable film-forming composition;and

(c) a curing agent comprising functional groups reactive with thereactive functional groups in (a); wherein the second film-formingpolymer (b) is more hydrophobic than the first film-forming polymer (a)and wherein upon application of the curable film-forming composition tothe substrate to form a coating layer, the first film-forming polymer(a) is distributed throughout the coating layer, and a concentration ofthe second film-forming polymer (b) is greater within a surface regionof the coating layer than a concentration of the second film-formingpolymer (b) within a bulk region of the coating layer; and wherein thecoated article demonstrates a transmission of electromagnetic radiationhaving a frequency of 22 to 81 GHz in the range of 70% to 100%, whereinthe vehicle component comprises at least one of a wheel, bumper, fender,hood, door, and panel.

In a thirteenth aspect, a method of mitigating contaminant build-up on asubstrate that is transparent to electromagnetic radiation having afrequency of 22 to 81 GHz, comprising:

(1) applying a first coating comprising a pigmented, curablefilm-forming composition to at least a portion of the substrate to forma coated substrate;

(2) applying a transparent, curable film-forming composition to at leasta portion of the coated substrate formed in step (1) prior tosubstantially curing the first coating to form a multi-layer coatedsubstrate, wherein the transparent, curable film-forming compositioncomprises:

(a) a first film-forming polymer having reactive functional groups andprepared from a reaction mixture which comprises at least onehydrophobic monomer present in the reaction mixture in an amount of 4 to15 percent by weight, based on the total weight of monomers in thereaction mixture, wherein the first film-forming polymer (a) is presentin the transparent, curable film-forming composition in an amount of 20to 40 percent by weight, based on the total weight of resin solids inthe curable film-forming composition;

(b) a second film-forming polymer different from the first film-formingpolymer (a) and prepared from a reaction mixture which comprises atleast one hydrophobic monomer comprising a siloxane, wherein thehydrophobic monomer in the reaction mixture used to prepare the secondfilm-forming polymer (b) is present in the reaction mixture in an amountof 15 percent by weight to 60 percent by weight, based on the totalweight of monomers in the reaction mixture, and wherein the secondfilm-forming polymer (b) is present in the transparent, curablefilm-forming composition in an amount of 0.5 to 15 percent by weight,based on the total weight of resin solids in the curable film-formingcomposition; and

(c) a curing agent comprising functional groups reactive with thereactive functional groups in (a); wherein the second film-formingpolymer (b) is more hydrophobic than the first film-forming polymer (a);and

(3) heating the multi-layer coated substrate formed in step (2) to atemperature and for a time sufficient to cure all the film-formingcompositions.

The following examples are intended to illustrate various embodiments ofthe invention, and should not be construed as limiting the invention inany way.

EXAMPLES

The following working examples are intended to further describe theinvention. It is understood that the invention described in thisspecification is not necessarily limited to the examples described inthis section.

Example A

A hydrophobic polyol to be used as a first film-forming polymer in thecomposition of the present invention, containing 4.8 percent by weightPDMS-functional methacrylate monomer, was synthesized by the followingprocedure. 2331 g amyl acetate was charged into a four-necked roundbottom flask fitted with a thermocouple, mechanical stirrer, andcondenser and blanketed with N₂. The mixture was heated to 150° C. andheld for 10 minutes. After that, an initiator mixture of 341 g amylacetate and 135 g LUPEROX 7M50 (polymerization initiator available fromArkema) was charged into the flask over 4 hours. Simultaneously, amonomer mixture of 407 g butyl methacrylate, 1035 g isobornylmethyacrylate, 635 g 2-hydroxyproyl methacrylate, 574 g hydroxyethylmethacrylate, 453 g butyl acrylate, 195 g KF-2012 silicone fluidavailable from Shin-Etsu and 87 g amyl acetate was charged into theflask over 3 hours. Directly after charging the above monomer mixture, asecond monomer mixture of 136 g butyl methacrylate, 211 g 2-hydroxyproylmethacrylate, 191 g hydroxyethyl methacrylate, 105 g butyl acrylate and39 g amyl acetate was charged into the flask over 45 minutes. After theinitiator mixture charge was complete, the reaction was held at 150° C.for an additional 30 minutes. After that, the system was cooled down to110° C., and 35 g butyl acrylate was charged into the flask all at once.A mixture of 142 g amyl acetate and 57 g LUPEROX 26 (polymerizationinitiator available from Arkema) was charged into the flask over 1 hour,followed by holding at 110° C. for 1 hour. The final measured solidcontent by weight of the above resin is 57.0% with a weight averagemolecular weight of 6498 g/mol and a number average molecular weight of2490 g/mol based on gel permeation chromatography using polystyrenestandards.

Example B

A hydrophobic polyol to be used as a second film-forming polymer in thecomposition of the present invention, containing 23.0 percent by weightpolydimethylsiloxane (PDMS)-functional methacrylate monomer wassynthesized by the following procedure. A mixture of 2404 g amylacetate, 841 g X-22-2426 (reactive silicone fluid available fromShin-Etsu), 534 g isobornyl methacrylate and 147g 4-hydroxybutylacrylate were charged into a four-necked round bottom flask fitted witha thermocouple, mechanical stirrer, and condenser and blanketed with N₂.The mixture was heated to 135° C. and held for 10 minutes. After that,an initiator mixture of 641 g amyl acetate and 140 g LUPEROX 7M50 wascharged into the flask over 3 hours. Simultaneously, a monomer mixtureof 1603 g isobornyl methyacrylate and 444 g 4-hydroxybutyl acrylate wascharged into the flask over 3 hours. After that, the reaction was heldat 135° C. for an additional 30 minutes. Then, a mixture of 320 g amylacetate and 32 g LUPEROX 26 was charged into the flask over 1 hour,followed by holding at 135° C. for 1 hour. The final measured solidcontent by weight of the above resin is 49.4% with a weight averagemolecular weight of 8300 g/mol and a number average molecular weight of1100 g/mol based on gel permeation chromatography using polystyrenestandards.

Formulation Example

A clear coat layer was applied over thermoplastic polyolefin (TPO)substrates. The coating layers were applied under controlled conditionsof 20-22° C. temperature and 60-65% relative humidity using conventionalspray equipment (SPRAYMATION, available from Spraymation, Inc). Thecoating layer was sprayed in two consecutive coats without anyintermediate drying between spray applications. The two coating layersof the clear coat system where then allowed to dry for 7 minutes underambient conditions and thereafter baked at 80° C. for 30 minutes. Thefilm thickness of system after final cure was approximately 50micrometers.

The clearcoat was prepared by mixing part A and B using the componentslisted on Table 1.

TABLE 1 Components Parts by weight n-Amyl Acetate 21.0 Diethylene Glycoln-butyl Ether Acetate 5.0 TINUVIN 928 ¹ 2.0 TINUVIN 292 ² 3.2 Melamine³7.2 Polysiloxane polyol silica ⁴ 4.1 Flow/anti-popping additive ⁵ 0.05Acrylic polyol ⁶ 17.6 Hydrophobic polyol of Example B 20.4 Hydrophobicpolyol of Example A 54.1 Saturated fatty acids ⁷ 4.0 SOLVESSO 100 ^(8 *)9.0 Crosslinker ⁹ * 40.0 Dibutyl Tin di-laurate ^(*) 0.15 ¹2-(2H-Benzotriazol-2yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenolUV absorber available from Ciba Specialty Chemicals Corp. ² Hinderedamine light stabilizer available from Ciba-Geigy Corp. ³Highly butylatedmelamine (CYMEL® 1156 available from Allnex) ⁴ Silica dispersionprepared as follows: a 4-neck reaction flask equipped for vacuumdistillation was flushed with N₂. To the reaction flask was added 1051.1parts-by-weight of a siloxane polyol, 1125.8 parts-by-weight ofORGANOSILICASOL MT-ST-M (colloidal silica from Nissan Chemicals), and480.3 parts-by-weight of methyl amyl ketone. The resulting mixture wasvacuum distilled at 25° C. for 4 hours. The siloxane polyol was preparedbeforehand by reacting 131.54 parts-by-weight of trimethylolpropanemonoallyl ether and 93.21 parts-by-weight of MASILWAX BASE (apolysiloxane-containing silicon hydride available from BASFCorporation). ⁵ Polyacrylate surface additive (BYK-390 by BYK) in butylacetate. ⁶ 14.5 percent by weight BMA; 14.5 percent by weight BA; 20percent by weight HEMA; 29 percent by weight IBOMA; 22 percent by weightHPMA at 53% weight solids in aromatic hydrocarbon mixture. ⁷ Prisorine3501 available from Croda ⁸ Blend of aromatic solvents available fromExxonMobil Corporation. ⁹ A mixture of 1.6 parts by weight DESMODURN-3300A (a 100% solids hexamethylene diisocyanate (HDI) trimer(isocyanurate ring) available from Covestro LLC) and 1 part by weightDESMODUR Z 44700 (a 70% solids isophorone diisocyanate (IPDI) trimer(isocyanurate ring) available from Covestro LLC). ^(*) Part of a B pack,mixed independently and added to the remaining of the ingredients beforeapplication.

The curable film-forming composition above was compared to a Controlclearcoat (DC4000 acrylic polyol mixed with DCH 3085 polyisocyanatehardener, both available from PPG). The Control clearcoat was appliedover thermoplastic polyolefin (TPO) using an HVLP gravity fed spray gun(SATA jet 4000) with a 12″ fan spray and 27 psi at the gun nozzle (1.8mm opening).

The TPO substrates with applied clearcoats were mounted betweenelectromagnetic radiation transmitter and receiver antennas with thecoated side of the substrate facing the transmitter. Water was sprayapplied to the coated substrates prior to measurement. The insertionloss (IL) was measured and referred to the amount of transmitted signalthat was not detected at the receiver. This method assumes a “lossless”condition in which the substrate either does not absorb or absorbs aninsignificant amount of the incident radar frequency. The % Transmissionwas calculated according to Equation 1. Substrates were tested using 24GHz, which is predominantly short-range radar, and 77 GHz, which ispredominantly long-range radar.% Transmission=100×10^(IL/10)  Equation 1.

TABLE 2 Radar testing of clearcoats Insertion loss % Transmission @ @ @@ Clearcoat 24 GHz 77 GHz 24 GHz 77 GHz Control with water −3.53 −3.2244.4 47.6 Control no water-dry −0.46 −0.57 89.9 87.7 Formulation Example−0.46 −1.23 89.9 75.3 with water Formulation Example −0.26 −0.73 94.284.5 no water-dry

Results collected for both short-range (24 GHz) and long-range (77 GHz)radar indicated that the coated article of the present inventioneffectively shed water and had significantly reduced insertion losscompared to the Control. This correlated to an improved radartransmission (Table 2). In fact, the % Transmission of the coatedarticle of the present invention with water was very close to thecoatings measured when they were dry, indicating a very effectivewater-shedding capability.

The extended retention of dirt and water build-up mitigation propertiesof the coated articles of the present invention compared to substratescoated with conventional compositions is due to a more homogenousdistribution of hydrophobic material throughout the coating, a propertythat is not possible with the sole use of traditional additive-typehydrophobic materials that are loaded at low concentrations (<10% finalsolids).

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the scope of the inventionas defined in the appended claims.

Therefore, we claim:
 1. A coated article comprising: (1) a substratethat is transparent to electromagnetic radiation having a frequency of22 to 81 GHz; and (2) a curable film-forming composition applied to atleast one surface of the substrate and cured thereon, the curablefilm-forming composition comprising: (a) a first film-forming polymerhaving reactive functional groups and prepared from a reaction mixturewhich comprises at least one hydrophobic monomer present in the reactionmixture in an amount of 4 to 15 percent by weight, based on the totalweight of monomers in the reaction mixture, wherein the firstfilm-forming polymer (a) is present in the curable film-formingcomposition in an amount of 20 to 40 percent by weight, based on thetotal weight of resin solids in the curable film-forming composition;(b) a second film-forming polymer different from the first film-formingpolymer (a) and prepared from a reaction mixture which comprises atleast one hydrophobic monomer comprising a siloxane, wherein thehydrophobic monomer in the reaction mixture used to prepare the secondfilm-forming polymer (b) is present in the reaction mixture in an amountof 15 percent by weight to 60 percent by weight, based on the totalweight of monomers in the reaction mixture, and wherein the secondfilm-forming polymer (b) is present in the curable film-formingcomposition in an amount of 0.5 to 15 percent by weight, based on thetotal weight of resin solids in the curable film-forming composition;and (c) a curing agent comprising functional groups reactive with thereactive functional groups in (a); wherein the second film-formingpolymer (b) is more hydrophobic than the first film-forming polymer (a)and wherein upon application of the curable film-forming composition tothe substrate to form a coating layer, the first film-forming polymer(a) is distributed throughout the coating layer, and a concentration ofthe second film-forming polymer (b) is greater within a surface regionof the coating layer than a concentration of the second film-formingpolymer (b) within a bulk region of the coating layer; and wherein thecoated article demonstrates a transmission of electromagnetic radiationhaving a frequency of 22 to 81 GHz in the range of 70% to 100%.
 2. Thecoated article of claim 1, wherein the hydrophobic monomer in thereaction mixture used to prepare the first film-forming polymer (a) isselected from at least one of a siloxane,2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluoroheptyl(meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Heneicosafluorododecyl(meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyl(meth)acrylate, 2,2,3,3,4,4,4-Heptafluorobutyl (meth)acrylate,2,2,3,4,4,4-Hexafluorobutyl (meth)acrylate,1,1,1,3,3,3-Hexafluoroisopropyl (meth)acrylate,2,2,3,3,4,4,5,5-Octafluoropentyl (meth)acrylate,2,2,3,3,3-Pentafluoropropyl (meth)acrylate, 1 H,1 H,2H,2H-Perfluorodecyl(meth)acrylate, 2,2,3,3-Tetrafluoropropyl (meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl (meth)acrylate,2,2,2-Trifluoroethyl (meth)acrylate, and2-[(1′,1′,1′-Trifluoro-2′-(trifluoromethyl)-2′-hydroxy)propyl]-3-norbornyl(meth)acrylate.
 3. The coated article of claim 1, wherein the reactionmixture used to prepare the second film-forming polymer (b) furthercomprises a monomer having a functional group reactive with thefunctional groups on the curing agent (c).
 4. The coated article ofclaim 1, wherein the curing agent (c) comprises a polyisocyanate.
 5. Thecoated article of claim 1, wherein the curable film-forming compositionfurther comprises (d) an additional film-forming resin component that(i) is different from the first and second film-forming polymers (a) and(b); and (ii) has functional groups that are reactive with at least oneother component of the curable film-forming composition.
 6. The coatedarticle of claim 5, wherein the additional film-forming resin component(d) comprises an acrylic and/or polyester polyol and an aminoplast. 7.The coated article of claim 1 wherein the curable film-formingcomposition is transparent to visible light.
 8. The coated article ofclaim 1, wherein the substrate comprises plastic and the curablefilm-forming composition further comprises (d′) a saturated fatty acidand (e) a tin catalyst.
 9. The coated article of claim 1, wherein thesubstrate comprises a component of a vehicle.
 10. The coated article ofclaim 9, wherein the vehicle comprises an autonomous vehicle.
 11. Thecoated article of claim 9, wherein the reaction mixture used to preparethe second film-forming polymer (b) further comprises a monomer having afunctional group reactive with the functional groups on the curing agent(c).
 12. A coated vehicle component comprising: (1) a substrate that istransparent to electromagnetic radiation having a frequency of 22 to 81GHz; and (2) a curable film-forming composition applied to at least onesurface of the substrate and cured thereon, the curable film-formingcomposition comprising: (a) a first film-forming polymer prepared fromat least one hydrophobic monomer and having reactive functional groups,present in the reaction mixture in an amount of 4 to 15 percent byweight, based on the total weight of monomers in the reaction mixture,and selected from at least one of a siloxane,2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluoroheptyl(meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Heneicosafluorododecyl(meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyl(meth)acrylate, 2,2,3,3,4,4,4-Heptafluorobutyl (meth)acrylate,2,2,3,4,4,4-Hexafluorobutyl (meth)acrylate,1,1,1,3,3,3-Hexafluoroisopropyl (meth)acrylate,2,2,3,3,4,4,5,5-Octafluoropentyl (meth)acrylate,2,2,3,3,3-Pentafluoropropyl (meth)acrylate, 1 H,1 H,2H,2H-Perfluorodecyl(meth)acrylate, 2,2,3,3-Tetrafluoropropyl (meth)acrylate,3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl (meth)acrylate,2,2,2-Trifluoroethyl (meth)acrylate, and2-[(1′,1′,1′-Trifluoro-2′-(trifluoromethyl)-2′-hydroxy)propyl]-3-norbornyl(meth)acrylate; wherein the first film-forming polymer (a) is present inthe curable film-forming composition in an amount of 20 to 40 percent byweight, based on the total weight of resin solids in the curablefilm-forming composition; (b) a second film-forming polymer differentfrom the first film-forming polymer (a) and prepared from a reactionmixture which comprises at least one hydrophobic monomer comprising asiloxane, wherein the hydrophobic monomer in the reaction mixture usedto prepare the second film-forming polymer (b) is present in thereaction mixture in an amount of 15 percent by weight to 60 percent byweight, based on the total weight of monomers in the reaction mixture,and wherein the second film-forming polymer (b) is present in thecurable film-forming composition in an amount of 0.5 to 15 percent byweight, based on the total weight of resin solids in the curablefilm-forming composition; and (c) a curing agent comprising functionalgroups reactive with the reactive functional groups in (a); wherein thesecond film-forming polymer (b) is more hydrophobic than the firstfilm-forming polymer (a) and wherein upon application of the curablefilm-forming composition to the substrate to form a coating layer, thefirst film-forming polymer (a) is distributed throughout the coatinglayer, and a concentration of the second film-forming polymer (b) isgreater within a surface region of the coating layer than aconcentration of the second film-forming polymer (b) within a bulkregion of the coating layer; and wherein the coated article demonstratesa transmission of electromagnetic radiation having a frequency of 22 to81 GHz in the range of 70% to 100%, wherein the vehicle componentcomprises at least one of a wheel, bumper, fender, hood, door, andpanel.
 13. A method of mitigating contaminant build-up on a substratethat is transparent to electromagnetic radiation having a frequency of22 to 81 GHz, comprising: (1) applying a first coating comprising apigmented, curable film-forming composition to at least a portion of thesubstrate to form a coated substrate; (2) applying a transparent,curable film-forming composition to at least a portion of the coatedsubstrate formed in step (1) prior to substantially curing the firstcoating to form a multi-layer coated substrate, wherein the transparent,curable film-forming composition comprises: (a) a first film-formingpolymer having reactive functional groups and prepared from a reactionmixture which comprises at least one hydrophobic monomer present in thereaction mixture in an amount of 4 to 15 percent by weight, based on thetotal weight of monomers in the reaction mixture, wherein the firstfilm-forming polymer (a) is present in the transparent, curablefilm-forming composition in an amount of 20 to 40 percent by weight,based on the total weight of resin solids in the curable film-formingcomposition; (b) a second film-forming polymer different from the firstfilm-forming polymer (a) and prepared from a reaction mixture whichcomprises at least one hydrophobic monomer comprising a siloxane,wherein the hydrophobic monomer in the reaction mixture used to preparethe second film-forming polymer (b) is present in the reaction mixturein an amount of 15 percent by weight to 60 percent by weight, based onthe total weight of monomers in the reaction mixture, and wherein thesecond film-forming polymer (b) is present in the transparent, curablefilm-forming composition in an amount of 0.5 to 15 percent by weight,based on the total weight of resin solids in the curable film-formingcomposition; and (c) a curing agent comprising functional groupsreactive with the reactive functional groups in (a); wherein the secondfilm-forming polymer (b) is more hydrophobic than the first film-formingpolymer (a); and (3) heating the multi-layer coated substrate formed instep (2) to a temperature and for a time sufficient to cure all thefilm-forming compositions.